Use of neutralizing agent in olefin or styrene production

ABSTRACT

The present invention generally relates to compositions and methods for neutralizing acidic streams in an olefin or styrene production plant. More specifically, the invention relates to neutralizing agents for dilution steam systems in the steam cracker process and their use for reducing acid corrosion and fouling in such systems.

FIELD OF THE INVENTION

The present invention generally relates to compositions and methods forneutralizing acidic streams in an olefin or styrene production plant.More specifically, the invention relates to neutralizing agents fordilution steam systems in the steam cracker process and their use forreducing acid corrosion, minimizing fouling and preventing productcontamination.

BACKGROUND OF THE INVENTION

Dilution steam is an integral component in the process of production ofethylene, propylene and other byproducts via the pyrolysis ofhydrocarbon feedstock. Dilution steam promotes the formation of desiredolefins by reducing the hydrocarbon partial pressure in the pyrolysisfurnace and it extends the run length of the furnace by slowing the rateof coke deposition.

After the hydrocarbon feedstock is pyrolyzed in the cracking furnace,the effluent gases must be rapidly cooled, i.e., quenched, in order toprevent the recombination of the reactive olefins into unwanted mixturesof oligomers, polymers and fused aromatic structures. During thisquenching process, steam is condensed and the resultant hot water isused for heat recovery, the water condensate is cooled further to beused in the quenching process, and a portion of the condensate isprocessed for re-use as dilution steam.

This “steam cracking” process (pyrolysis of hydrocarbon feedstock in thepresence of dilution steam) also produces a small quantity of lessdesirable by-products such as carbon monoxide, carbon dioxide,acetaldehyde, and acetic acid. The organic acids, acetic acid, propionicacid, formic acid, and to a lesser extent higher C₄-C₆ organic acidspromote corrosion in the aqueous environs of the quench water system,the quench water cleaning vessels (oil/water separator, coalescers,process water stripper) and the dilution steam generator. Anothercontributor to acidic conditions in the “dilution steam system” (asystem which includes the quench water system, oil/water separator,process water stripper, dilution steam generator and dilution steampiping) are sulfur-based acids, formed from cracking of sulfur compoundsthat come with or are added to the hydrocarbon feedstock. These acidicbyproducts are neutralized with an alkaline agent.

In many systems, the neutralizing agent of choice for dilution steamsystems was caustic, NaOH, and this alkalizer is cost-effective providedthat the dilution steam generator has sufficient size or design featuresthat prevent the incidental carry-over of sodium ions with the dilutionsteam. Low levels of carry-over of sodium with the dilution steam cancause a greater degree of furnace coking and shorter furnace run length,while high levels of carry-over of sodium can destroy the mechanicalproperties of the furnace radiant tubes (e.g., sodium embrittlement).

To circumvent the hazards associated with sodium carry-over, a largenumber of ethylene producers have opted to control pH in the dilutionsteam system with the use of neutralizing amines. Althoughmonoethanolamine (MEA) is a cost-effective amine, it reacts with aceticacid in dilution steam condensate to form MEA-acetate salt. In anaqueous solution, this salt generates a buffered pH condition wherein asmall addition of acid does not greatly decrease the pH and a smalladdition of base does not greatly increase the pH. Even though thisbuffering condition protects against pH shifts into the more corrosiveacidic regime, it also requires use of large amounts of MEA to raise thepH into the protective pH range to avoid solubilization of iron oxidesand thereby prevent corrosion.

Even though MEA has a relatively low volatility ratio in a steam boiler,some amine will carry over with the steam phase in the boiler. When anamine, such as MEA, goes to the pyrolysis furnace, the amine is crackedto form ammonia and hydrocarbon by-products. Ammonia is a contaminantfor the ethylene product because it poisons the catalysts that are usedto produce polyethylene and ethylene copolymers. When ethylene productis off-specification due to ammonia, the ethylene product is sentdirectly to the flaring system until the product is back onspecification. Since ammonia is a base, it can raise the pH in thequench water of the dilution steam system. If the addition of theammonia is uncontrolled, then the quench water can become too alkalineand can promote stabilized emulsions in the quench oil/water separator,causing premature fouling of the dilution steam generator.

Thus, a need for a more effective neutralizer exists.

SUMMARY OF THE INVENTION

One aspect of the invention is a method for inhibiting fouling andcorrosion of equipment in an ethylene production plant. The methodcomprises injecting a neutralizing agent into a dilution steam system,the neutralizing agent having a volatility index of less than 0.005, anda pKa of about 12 to about 20. The neutralizing agent further beingsubstantially sodium-free and when the neutralizing agent is a cholinesalt, the choline salt is stabilized by about 2 wt. % to about 10 wt. %alkanolamine.

Another aspect of the invention is a method for inhibiting fouling andcorrosion of equipment in a styrene production plant. The methodcomprises injecting a neutralizing agent into a dilution steam system,the neutralizing agent having a volatility index of less than 0.005 anda pKa of about 12 to about 20, and being substantially sodium-free.

Yet another aspect is a method for inhibiting fouling and corrosion ofequipment in an ethylene or styrene production plant. The methodcomprises injecting a neutralizing agent into a dilution steam system.The neutralizing agent comprises a choline salt stabilized by about 2wt. % to about 10 wt. % alkanolamine.

A further aspect of the invention is a stabilized choline compositionthat comprises a choline salt, a solvent, and from about 2 wt. % toabout 10 wt. % of an alkanolamine based on the total weight of thecomposition.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of an olefin dilution steam system.

FIG. 2 is a schematic of a styrene dilution steam system.

FIG. 3 is a graph of pH versus concentration of neutralizing agent for100% w/w monoethanolamine (MEA), 66.4% w/w MEA, 39.6% w/w cholinehydroxide and 12% w/w MEA, 41% w/w choline hydroxide and 9% w/w MEA,42.3% w/w choline hydroxide and 6% w/w MEA, and 43.4% w/w cholinehydroxide and 3% w/w MEA.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Neutralizing agents for ethylene and styrene production plants have beendiscovered to effectively prevent or reduce fouling of the equipmentwith undesirable hydrocarbon deposits and to inhibit productcontamination. Such neutralizing agents have a relatively high pKa and arelatively low volatility index (V/L) and are substantially sodium-free.

The high pKa allows the neutralizing agent to be effective at increasingthe pH of the aqueous solution in the dilution steam system whileminimizing the amount of neutralizing agent needed. In selecting aneutralizing agent with a high pKa, once the acids arestoichiometrically neutralized, only a small excess of the high pKaneutralizer is needed to increase the pH of the boiler water. The highpKa of the neutralizing agent helps to reduce the level of treatmentneeded in the waste water system since it allows for a smaller amount ofthe neutralizing agent to be used.

Due to the low volatility of the neutralizing agent, it is less likelythat the neutralizing agent will go with the steam phase in the boiler.Since the neutralizing agent is less likely to be in the steam phase,the neutralizing agent is also less likely to reach the pyrolysisfurnace. When an amine used as a neutralizing agent enters the pyrolysisfurnace, it is cracked to form ammonia and hydrocarbons. The ammonia isa contaminant in the ethylene product because it poisons thepolymerization catalysts. Ammonia can also increase the pH of the quenchwater, but when the ammonia addition is uncontrolled, the quench watercan reach a pH that is too high and emulsions can form that impede theseparation of the oil and water. The low volatility of the neutralizingagent avoids formation of these emulsions which can cause fouling of thedilution steam generator.

The neutralizing agent is sodium-free or substantially sodium-free sothat carry over of sodium ions into the furnace does not occur or isminimal. Such carry over can cause furnace coking, shorter furnace runlength, or sodium embrittlement of the furnace radiant tubes. The sodiumembrittlement makes the radiant tubes become like glass andsignificantly reduces the useful life of the furnace radiant tubes. Aneutralizing agent is “substantially sodium-free” if the neutralizingagent or a composition comprising the neutralizing agent contains anamount of sodium that does not result in furnace coking or result insodium embrittlement in any component of the dilution steam system.Preferably, the neutralizing agent is sodium-free.

A method of the invention inhibits fouling and corrosion of equipment inan ethylene production plant and comprises injecting a neutralizingagent into a dilution steam system, the neutralizing agent having avolatility index of less than 0.005 and a pKa of about 12 to about 20,and being substantially sodium-free.

A method for inhibiting fouling and corrosion of equipment in anethylene production plant, the method comprising injecting aneutralizing agent into a dilution steam system, the neutralizing agentcomprising a choline salt stabilized by about 2 wt. % to about 10 wt. %alkanolamine.

The process of cracking a hydrocarbon feed produces the desired olefins,primarily C₂-C₄ olefins such as ethylene, propylene, butylene, andbutadiene. The cracking process also produces by-products such as carbonmonoxide, carbon dioxide, acetaldehyde, and organic acids such as aceticacid, propionic acid, formic acid and some C₄ to C₆ organic acids. Also,some sulfur-based acids are products of the cracking of sulfur compoundscontained in the hydrocarbon feed. Addition of the neutralizing agentinto the dilution steam system reduces damage to the system that can becaused by the presence of some of these by-products as described in moredetail above.

The dilution steam system used in the methods described herein cancomprise a furnace, a quench water tower, a quench water separator, acoalescer, a process water stripper, and a dilution steam generator. Arepresentative dilution steam system for ethylene production is shown inFIG. 1, in which a hydrocarbon feedstock 10 is fed into a pyrolysisfurnace 12 and the effluent from the pyrolysis furnace contained in aneffluent line 14 is fed to a quench water tower 20. The quench watertower 20 reduces the temperature of the gases in the overhead line 24 byspraying cool water from the top of the quench water tower 20. Thisprocess recovers energy, reduces undesirable side reactions, andcondenses a fraction of the pyrolysis gas. The quench water towerbottoms are contained in a quench water tower line 22 and are sent tothe quench water separator 30. The quench water separator 30 separateshydrocarbons from water and is the first step in cleaning the waterexiting the quench water tower. Light hydrocarbons are contained in alight hydrocarbons line 34 and are separated from the water contained inthe quench water separator line 32 that is sent to the coalescer unitcomprising filters 36 and a coalescer 40. The coalescer unit furtherimproves the quality of the process water by removing organic and solidmaterials by using the filters 36 to recover solids and the coalescer 40to reduce hydrocarbons. The water contained in the quench waterseparator line 32 from the quench water separator 30 is first sent tothe filters 36 of the coalescer unit and after filtering the watercontained in the filter line 38 is sent to the coalescer 40. Thecoalescer 40 separates light oils from water. The light oils containedin the light oil line 44 from the coalescer are sent to the quench waterseparator 30 and the water from the coalescer contained in the coalescerline 42 is sent to the process water stripper 50. The process waterstripper 50 purifies the process water by removing hydrogen sulfide,carbon dioxide, ammonia, and light hydrocarbons. The gases contained inthe gas line 54 are typically sent to the quench water tower 20 and thebottoms contained in the process water stripper line 52 from the processwater stripper 50 are sent to the dilution steam generator 60. Dilutionsteam makeup 56 can be added to the process water stripper 50 as needed.The dilution steam generator 60 generates dilution steam using quenchoil or medium pressure steam. The steam drum in the dilution steamgenerator 60 contains a demister pad to eliminate carry over ofimpurities and the impurities are purged via the blow down 64. Thetreated dilution steam 62 is directed to the feed line 10 to recycledilution steam back into the pyrolysis furnace 12.

The neutralizing agent can be injected at one or more points within thedilution steam system for ethylene production. The neutralizing agentcan be injected into the process water stripper line between the processwater stripper and the dilution steam generator at a concentration tokeep the aqueous solution in the dilution steam generator at a pHbetween about 9 and about 12, preferably between about 9.5 and about10.5, thereby reducing corrosion or fouling of the dilution steamgenerator. For example in FIG. 1, an injection of the neutralizing agentinto a dilution steam generator injection point 58 into the processwater stripper line 52 can be made to maintain the pH of the aqueoussolution in the dilution steam generator 60 at between about 9 and about12, preferably between about 9.5 and about 10.5.

The neutralizing agent can be injected into the quench water tower linebetween the quench water tower and the quench water separator at aconcentration to keep the aqueous solution in the quench water separatorat a pH between about 5.5 and 7.5, thereby reducing corrosion of thequench water separator. For example in FIG. 1, an injection of theneutralizing agent at a quench water separator point 28 into the quenchwater tower line 22 can be made to provide the aqueous solution in thequench water separator 30 with a pH between about 5.5 and about 7.5.

The neutralizing agent can be injected into the quench water separatorline between the coalescer and the process water stripper at aconcentration to keep the aqueous solution in the process water stripperat a pH between about 8 and 9, thereby reducing corrosion or fouling ofthe process water stripper, and reducing ammonia contamination of thevapor exiting the process water stripper. For example in FIG. 1, aninjection of the neutralizing agent at a process water stripperinjection point 48 into the coalescer line 42 can be made to maintainthe aqueous solution in the process water stripper 50 at a pH betweenabout 8 and about 9.

Another aspect of the invention is a method for inhibiting fouling andcorrosion of equipment in an ethylene production plant. The methodcomprises injecting a neutralizing agent comprising a choline salt intoa dilution steam system. The dilution steam system comprises a furnace,a quench water tower, a quench water separator, a coalescer, a processwater stripper, and a dilution steam generator and the neutralizingagent is injected (i) into a process water stripper line between theprocess water stripper and the dilution steam generator at aconcentration to keep the aqueous solution in the dilution steamgenerator blowdown at a pH between about 9 and about 12, therebyreducing corrosion or fouling of the dilution steam generator; (ii) intoa quench water tower line between the quench water tower and the quenchwater separator at a concentration to keep the aqueous solution in thequench water separator at a pH between about 5.5 and 7.5, therebyreducing corrosion of the quench water separator; and (iii) into acoalescer line between the coalescer and the process water stripper at aconcentration to keep the aqueous solution in the process water stripperbottom discharge at a pH between about 8 and 9, thereby reducingcorrosion or fouling of the process water stripper, and reducing ammoniacontamination of the vapor exiting the process water stripper.

A method of the invention inhibits fouling and corrosion of equipment ina styrene production plant and comprises injecting a neutralizing agentinto a dilution steam system, the neutralizing agent having a volatilityindex of less than 0.005 and a pKa of about 12 to about 20, and beingsubstantially sodium-free.

A method for inhibiting fouling and corrosion of equipment in an styreneproduction plant, the method comprising injecting a neutralizing agentinto a dilution steam system, the neutralizing agent comprising acholine salt stabilized by about 2 wt. % to about 10 wt. % alkanolamine.

A representative dilution steam system for styrene production is shownin FIG. 2, in which an ethyl benzene feedstock in a feed line 106 ismixed with superheated steam from a superheater line 112 and fed vialine 108 to a reactor 120 and reacted. The effluent from the reactorcontained in a reactor line 122 is directed to a series of heatexchangers (e.g., heat exchanger 130, heat exchanger 134, and heatexchanger 138) to cool and condense the reactor effluent. The contentsof heat exchanger 130 are directed to heat exchanger 134 through heatexchanger line 132, the contents of heat exchanger 134 are directed toheat exchanger 138 through the heat exchanger line 135. The contents ofheat exchanger 138 are transferred through the heat exchanger line 139to the separator 140, which separates vent gas from condensate and crudestyrene. The vent gas from the separator 140 is directed through thevent gas line 142 to a gas/liquid separator 150 and the vent gas fromthe vent gas condenser is directed through a vent gas condenser line 154to a vent gas compressor 156. The compressed vent gas is directedthrough a compressor line 157 to a compressor heat exchanger 158 andsent as an off gas through the off gas line 159.

The condensate from the separator 140 is directed through the separatorline 146 to the process water stripper 160. The process water stripperbottoms are directed through a process water stripper line 162 to adilution steam generator 170. The steam from the dilution steamgenerator 170 can be directed through a dilution steam generator line176 to a superheater 110. The steam released from the superheater 110 isdirected through a superheater line 112 into the reactor 120 to reactwith the ethyl benzene.

The neutralizing agent can be injected at one or more points within thedilution steam system for styrene production. A neutralizing agent canbe injected into a heat exchanger line between two heat exchangers at aconcentration to keep the condensate from the separator at a pH betweenabout 6.5 and about 7.5, thereby reducing corrosion or fouling of theheat exchanger or separator. For example in FIG. 2, an injection ofneutralizing agent can be made into the heat exchanger line 135 at heatexchanger injection point 136 to maintain the aqueous solution in theseparator 140 at a pH between about 6.5 and about 7.5.

Further, a neutralizing agent can be injected into a vent gas linebetween the separator and the vent gas condenser at a concentration tokeep vent gas condenser condensate at a pH between about 6.5 and 7.5,thereby reducing corrosion of the vent gas compressor. For example inFIG. 2, a neutralizing agent can be injected into the vent gas line 142at vent gas injection point 144 to maintain the pH of the condensate inthe vent gas condenser 150 at a pH between about 6.5 and 7.5.

Additionally, a neutralizing agent can be injected into a separator linebetween the separator and the process water stripper at a concentrationto keep the aqueous solution in the process water stripper bottoms at apH between about 8.8 and 9.2, thereby reducing corrosion or fouling ofthe process water stripper, and reducing ammonia contamination of thevapor exiting the process water stripper. For example in FIG. 2, aneutralizing agent can be injected into the separator line 146 at aseparator line injection point 148 to maintain the pH of the aqueoussolution in the process water stripper 160 is from about 8.8 to about9.2.

Also, a neutralizing agent can be injected into a process water stripperline between the process water stripper and the dilution steam generatorat a concentration to keep the dilution steam generator blow down at apH between about 9.5 and 10.5, thereby reducing corrosion of thedilution steam generator. For example in FIG. 2, an injection of theneutralizing agent can be made into the process water stripper line 162at a process water stripper injection point 164 to maintain the pH ofthe aqueous solution in the dilution steam generator 170 at a pH fromabout 9.5 to about 10.5.

Another aspect of the invention is a method for inhibiting fouling andcorrosion of equipment in a styrene production plant. The methodcomprises injecting a neutralizing agent comprising a choline salt intoa dilution steam system, wherein the dilution steam system comprises asuper heater, a reactor, a plurality of heat exchangers, a separator, avent gas condenser, a vent gas compressor, a process water stripper, anda dilution steam generator and wherein the neutralizing agent isinjected (i) into a heat exchanger line between two heat exchangers at aconcentration to keep the condensate from the separator at a pH betweenabout 6.5 and about 7.5, thereby reducing corrosion or fouling of theheat exchanger or separator; (ii) into a vent gas line between theseparator and the vent gas condenser at a concentration to keep vent gascondenser condensate at a pH between about 6.5 and 7.5, thereby reducingcorrosion of the vent gas compressor; (iii) into a separator linebetween the separator and the process water stripper at a concentrationto keep the aqueous solution in the process water stripper bottoms at apH between about 8.8 and 9.2, thereby reducing corrosion or fouling ofthe process water stripper, and reducing ammonia contamination of thevapor exiting the process water stripper; and (iv) into a process waterstripper line between the process water stripper and the dilution steamgenerator at a concentration to keep the dilution steam generator blowdown at a pH between about 9 and about 12, preferably between about 9.5and about 10.5, thereby reducing corrosion of the dilution steamgenerator.

The relationship between corrosion control and operating pH is straightforward: acidic pH conditions are corrosive, while alkaline conditionscause less corrosion. The relationship between pH control and fouling isnot as straightforward. For the ethylene cracking process, high pH inthe quench water tower and oil/water separator increases the formationof stable hydrocarbon/water emulsions. The composition of pyrolysisgasoline can contain numerous reactive olefins and diolefins that areprone to polymerization reactions. The process conditions and reactantsin the process water stripper can promote polymerization while solventremoval from emulsions not resolved in the oil/water separator takesplace. In turn, this polymer production and solvent removal can lead tofoulant (e.g., hydrocarbon polymers) deposition in the bottom of theprocess water stripper and in the dilution steam generator.

When traditional amines, most often alkanolamines, are used as steamdilution system neutralizing agents, the initial control of quench waterpH poses no problems. However, during and after this initial period ofoperation, a small amount of amine can travel with the dilution steamand can be pyrolyzed in the furnace, thus generating ammonia. Sinceammonia is a volatile alkalizing agent, when formed, it accumulates inthe quench water tower and in the oil/water separator. This ammoniaaccumulation causes the quench water pH to rise above the desired pH setpoint and the elevated pH promotes the formation of stable emulsions.When the ammonia accumulation exceeds the saturation limits of thequench water system, the ammonia can travel with the cracked gas towardsthe purification system. The ammonia distills with the ethylene fractionand can contaminate the final product. Thus, providing controls for theammonia produced in the ethylene process is advantageous.

The volatility index (or V/L ratio) of the neutralizing agent is themeasure of the partition of the neutralizing agent between the vapor andliquid state at a particular pressure. The volatility index isdetermined by operating a small boiler unit. The boiler is charged withde-ionized water and a measured amount of the neutralizing agent isadded to the water. The boiler is heated to a specified pressure andwhen steady-state at that pressure is achieved, a sample of steam iscondensed and collected and simultaneously a sample of the boiler wateris collected. The two water samples are then analyzed for theneutralizing agent concentration. The volatility index is thencalculated by dividing the concentration of the neutralizing agent inthe steam by the concentration of the neutralizing agent in the water.Then, the boiler is heated further to the next desired pressure and whensteady-state is achieved, another set of samples is collected.

The neutralizing agent can comprise a choline salt. Preferably, thecholine salt is choline hydroxide.

When the neutralizing agent is a choline salt, the choline salt can beadvantageously stabilized to provide a stabilized choline compositioncomprising a choline salt, a solvent, and from about 2 wt. % to about 10wt. % of an alkanolamine based on the total weight of the composition.

The stabilized choline composition can have a concentration of cholinesalt from about 10 wt. % to about 50 wt. %, from about 15 wt. % to about30 wt. %, from about 15 wt. % to about 25 wt. %, or about 20 wt. % basedon the total weight of the composition.

The stabilized choline composition can comprise an alkanolamine such asmethanolamine, ethanolamine (i.e., monoethanolamine (MEA)),propanolamine, butanolamine, or a combination thereof. Preferably, thealkanolamine is methanolamine, ethanolamine, or a combination thereof.More preferably, the alkanolamine comprises ethanolamine (MEA).

The stabilized choline composition can comprise the alkanolamine in aconcentration from about 3 wt. % to about 8 wt. %, about 4 wt. % toabout 6 wt. %, or about 5 wt. % based on the total weight of thecomposition.

The solvent in the stabilized choline composition can comprise water.

In operational practice, an ethylene plant is a dynamic process withminor shifts in feedstock composition, process flow rates, temperaturefluctuations, and other process conditions and as a result, theconcentration of acids to be neutralized is can vary slightly. Thepreferred, stabilized neutralizing agent of this invention isadditionally advantageous because the relationship between the pH of thesolution and the concentration of neutralizing agent used (i.e., theneutralization profile) goes from a nearly vertical rise in pH at pHs of9 and below to a less steep pH rise when concentration of theneutralizing agent keeps the solution between pH 9 to 12, preferably,between pH 9.5 to 10.5. This pH target of 9 to 12, preferably, pH 9.5 to10.5 is sought in the dilution steam generator, where corrosion is thegreatest concern. This neutralizing profile for the neutralizing agentdescribed herein means that less of the neutralizing agent is needed tomaintain the solution it is used to neutralize (e.g., dilution steam) atthe desired pH.

The neutralizing agent can be injected into the system in a variety ofways known to a person of skill in the art. The injection control may bea microprocessor, a central process unit, or any other similar devicecapable of processing the signal output from the acid measurement deviceand controlling the rate of dispensation of the neutralizing agent inresponse to this signal. The injection control may be integral with theneutralizing agent injector or it may be separate. Suitable injectioncontrollers would include control systems that are well known in theart.

The acid concentration detector may be any one of a number of devicescapable of generating a signal responsive to the concentration of acidin the dilution steam system. Automated titrators are particularlyeffective acid measuring devices. A number of automated titratorssuitable for use in the system are commercially available includingthose from Rosemount Inc., Honeywell, Hach, or Mettler Toledo.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims.

EXAMPLES

The following non-limiting examples are provided to further illustratethe present invention.

Example 1 Titration of 1300 Ppm of Acetic Acid with Neat Ethanolamine(MEA)

To test the comparative neutralization efficacy of MEA as a neutralizer,the solution was initially diluted according to the following procedure.Into a glass container was added 10.0 g of neat MEA. This was diluted toa total mass of 500 g using deionized water.

A solution of 1300 ppm acetic acid was prepared by adding 0.652 g of99.7% (purity) glacial acetic acid to a 500 mL volumetric flask. To thisflask was added deionized water to give 500 mL of final solution. A 30mL aliquot of this solution was added to a 100 mL titration vial. Usinga pH meter, the initial pH of this solution was measured. Thereafter,the diluted solution of neat MEA was added to the vial in smallquantities at a time while the pH of the solution was measured at everypoint. The titration was continued until the solution had the target pHof 10.5. To reach this pH, 8154 ppm of the neutralizer was required.

Example 2 Titration of 1300 Ppm of Acetic Acid with Choline Hydroxide

In the second example of comparative neutralization, 45% (w/w) cholinehydroxide was initially diluted prior to the titration with 1300 ppm ofacetic acid according to the procedure in Example 1. The titration wascontinued until the solution had the target pH of 10.5; 4820 ppm of theneutralizer was required to reach this pH.

Example 3 Boiler-MEA Formulation Neutralization of Acetic Acid

At the temperature at which the ethylene plant boiler is operated, MEAis volatile such that a third of the neutralizer evaporates beforeneutralizing the acids in the water. To mimic the concentration of theMEA left in the boiler, a formulation containing 66.4% (w/w) of MEA and33.6% (w/w) deionized water was prepared. This formulation was used toneutralize 30 mL of 1300 ppm acetic acid following the procedure inExample 1. To reach the target pH of 10.5, a total amount of 9792 ppm ofthe neutralizer formulation was added to the acetic acid solution.

Example 4 Titration of 1300 Ppm of Acetic Acid with Heavy NeutralizerFormulations

Heavy neutralizer formulations were prepared by blending MEA with 45%(w/w) choline hydroxide. By way of example, the heavy neutralizerformulation was prepared by adding 3 g of ethanolamine (MEA) to a glassbottle containing 97 g of an aqueous solution of 45% (w/w) cholinehydroxide. This contained 3% (w/w) of MEA and 43.4% % (w/w) of cholinehydroxide solution. As in Example 1, 10 g of this neutralizer wasinitially diluted with deionized water yield a total mass of 500 g.

The same stock solution of 1300 ppm acetic acid prepared in Example 1was used for the titration with the diluted solution of the heavyneutralizer comprising 3% (w/w) MEA and 43.4% (w/w) of cholinehydroxide. Similar to Example 2, the diluted solution of the heavyneutralizer formulation was added in small quantities while monitoringthe pH of the solution after each addition of the neutralizer until thepH of the solution was basic and the pH plateaued off. A totalconcentration of 4846 ppm of this heavy neutralizer was consumed toattain the pH of 10.5.

Other formulations were similarly prepared, diluted and titrated against1300 ppm of acetic acid. The formulation compositions and concentrationsrequired to reach the pH condition of 10.5 are shown in the table below.Titration curves of some of the formulations are shown in FIG. 3.

Heavy neutralizer formulations and amount (ppm) required to keep asolution of 1300 ppm acetic acid at a pH of 10.5.

% (w/w) % (w/w) ppm of Base MEA Choline Hydroxide (to keep pH of 10.5)100 0.0 8154 66.4* 0.0 9792 30.0 31.9 5434 12.0 39.6 5080 9.0 41.0 51676.0 42.3 4868 3.0 43.4 4846 0.0 45.0 4820 *Percentage of MEA in boilerafter the evaporation of some of the injected MEA.

Example 5 Stability of Treated and Untreated Choline Hydroxide SolutionsStored at Room Temperature

To a sample of 96 g aqueous choline hydroxide solution (20.3 wt. %) wasadded 4.0 g ethanolamine. No ethanolamine was added to a second sample.The samples were stored in a fume hood at 25° C. for a period ofapproximately 12 months. The decomposition of the samples over time wasmonitored using a spectrophotometer (λ_(max)=410 nm). Upondecomposition, the initial colorless solutions of choline hydroxideturned yellow; as decomposition progressed, the solutions turned brown.In addition to the change in color, the decomposition process resultedin the formation of suspended, and then settled solids.

Example 6 Stability of Treated and Untreated Choline Hydroxide SolutionsIncubated at 55° C. For 397 Days

To a sample of 96 g aqueous choline hydroxide solution (20 wt. %) wasadded 4.0 g ethanolamine. To a second sample no MEA was added. Anadditional untreated sample of aqueous choline hydroxide (45 wt. %) wasalso prepared. The three samples were then incubated at a temperature of55° C. for a period of 397 days.

After 397 days, the three samples were removed from the incubator andvisually inspected. The untreated 45 wt. % choline hydroxide sample hada brown supernatant and brown sediment at the bottom of the container.The untreated 20 wt. % choline hydroxide sample also had a brownsupernatant but less brown sediment was observed. The treated 20 wt. %choline hydroxide sample did not have any sediment, and was pale amberin color.

Using a spectrophotomer, undiluted aliquots of the treated and untreated20 wt. % choline hydroxide solutions were analyzed for decomposition atan absorbance of 410 nm. Absorbance of the treated sample was 2.850,whereas absorbance of the untreated sample was 3.315. Additionalabsorbance measurements were then taken using 0.5 mL aliquots of eachsample that had been diluted with 9.5 mL of deionized water. Absorbanceof the treated diluted sample was 0.380, and absorbance of the untreateddiluted sample was 0.786.

Example 7 Stability of Treated and Untreated Choline Hydroxide SolutionsIncubated at 55° C. For 20 Days

A stock solution of aqueous choline hydroxide (20.83 wt. %) was preparedby dilution of 40.195 g aqueous choline hydroxide solution (45 wt. %)with 48.552 g deionized water. To a sample of 24.0 g of the stocksolution was added 1.0 g ethanolamine. To a second sample of 24.0 g ofthe stock solution was added 1.0 g deionized water. The samples werethen incubated at 55° C. At intervals, 0.5 mL aliquots of each samplewere retrieved and diluted with 9.5 mL deionized water, then theirabsorbance measured at λ_(max)=410 nm. Aliquots were taken at T=0, 3, 8,10, 16, and 20 days. The absorbance data for the treated and untreatedsamples of aqueous choline hydroxide solution as a function of time isshown in the table below.

Incubation 20% Choline 20% Choline Days Bases (Untreated) Base (Treated)0 0.004 0.004 3 0.016 0.008 8 0.048 0.019 10 0.053 0.02 16 0.063 0.03320 0.088 0.042 397 0.786 0.380

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained.

As various changes could be made in the above compositions and methodswithout departing from the scope of the invention, it is intended thatall matter contained in the above description and shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A method for inhibiting fouling and corrosion ofequipment in an ethylene or styrene production plant, the methodcomprising injecting a neutralizing agent into a dilution steam system,the neutralizing agent being substantially sodium-free, and comprising acholine salt stabilized by about 2 wt. % to about 10 wt. % alkanolamine.2. The method of claim 1 wherein the alkanolamine comprisesethanolamine.
 3. The method of claim 1 wherein the choline salt ischoline hydroxide.
 4. A method for inhibiting fouling and corrosion ofequipment in an ethylene or styrene production plant, the methodcomprising injecting a neutralizing agent into a dilution steam system,the neutralizing agent having a volatility index of less than 0.005, anda pKa of about 12 to about 20, and being substantially sodium-free,wherein when the neutralizing agent is a choline salt, the choline saltis stabilized by about 2 wt. % to about 10 wt. % alkanolamine, whereinthe dilution steam system of the ethylene production plant comprises afurnace, a quench water tower, a quench water separator, a coalescer, aprocess water stripper, and a dilution steam generator and wherein theneutralizing agent is injected either (i) into a process water stripperline between the process water stripper and the dilution steam generatorat a concentration to keep the aqueous solution in the dilution steamgenerator blowdown at a pH between about 9 and about 12, therebyreducing corrosion or fouling of the dilution steam generator; (ii) intoa quench water tower line between the quench water tower and the quenchwater separator at a concentration to keep the aqueous solution in thequench water separator at a pH between about 5.5 and 7.5, therebyreducing corrosion of the quench water separator; or (iii) into acoalescer line between the coalescer and the process water stripper at aconcentration to keep the aqueous solution in the process water stripperbottom discharge at a pH between about 8 and 9, thereby reducingcorrosion or fouling of the process water stripper, and reducing ammoniacontamination of the vapor exiting the process water stripper.
 5. Themethod of claim 4 wherein the neutralizing agent is injected into theprocess water stripper line between the process water stripper and thedilution steam generator at a concentration to keep the aqueous solutionin the dilution steam generator at a pH between about 9.5 and about10.5, thereby reducing corrosion or fouling of the dilution steamgenerator.
 6. The method of claim 4 wherein the neutralizing agent isinjected into the quench water tower line between the quench water towerand the quench water separator at a concentration to keep the aqueoussolution in the quench water separator at a pH between about 5.5 and7.5, thereby reducing corrosion of the quench water separator.
 7. Themethod of claim 4 wherein the neutralizing agent is injected into thecoalescer line between the coalescer and the process water stripper at aconcentration to keep the aqueous solution in the process water stripperat a pH between about 8 and 9, thereby reducing corrosion or fouling ofthe process water stripper, and reducing ammonia contamination of thevapor exiting the process water stripper.
 8. A method for inhibitingfouling and corrosion of equipment in an ethylene or styrene productionplant, the method comprising injecting a neutralizing agent into adilution steam system, the neutralizing agent having a volatility indexof less than 0.005, and a pKa of about 12 to about 20, and beingsubstantially sodium-free, wherein when the neutralizing agent is acholine salt, the choline salt is stabilized by about 2 wt. % to about10 wt. % alkanolamine, wherein the dilution steam system of the styreneproduction plant comprises a super heater, a reactor, a plurality ofheat exchangers, a separator, a vent gas condenser, a vent gascompressor, a process water stripper, and a dilution steam generator andwherein the neutralizing agent is injected either (i) into a heatexchanger line between two heat exchangers at a concentration to keepthe condensate from the separator at a pH between about 6.5 and about7.5, thereby reducing corrosion or fouling of the heat exchanger orseparator; (ii) into a vent gas line between the separator and the ventgas condenser at a concentration to keep vent gas condenser condensateat a pH between about 6.5 and about 7.5, thereby reducing corrosion ofthe vent gas compressor; (iii) into a separator line between theseparator and the process water stripper at a concentration to keep theaqueous solution in the process water stripper bottoms at a pH betweenabout 8.8 and about 9.2, thereby reducing corrosion or fouling of theprocess water stripper, and reducing ammonia contamination of the vaporexiting the process water stripper; or (iv) into a process waterstripper line between the process water stripper and the dilution steamgenerator at a concentration to keep the dilution steam generator blowdown at a pH between about 9 and about 12, thereby reducing corrosion ofthe dilution steam generator.
 9. The method of claim 8 wherein theneutralizing agent is injected into the heat exchanger line between twoheat exchangers at a concentration to keep the condensate from theseparator at a pH between about 6.5 and about 7.5, thereby reducingcorrosion or fouling of the heat exchanger.
 10. The method of claim 8wherein the neutralizing agent is injected into the vent gas linebetween the separator and the vent gas condenser at a concentration tokeep the vent gas condenser condensate at a pH between about 6.5 andabout 7.5, thereby reducing corrosion of the vent gas compressor. 11.The method of claim 8 wherein the neutralizing agent is injected intothe separator line between the separator and the process water stripperat a concentration to keep the aqueous solution in the process waterstripper bottoms at a pH between about 8.8 and about 9.2, therebyreducing corrosion or fouling of the process water stripper, andreducing ammonia contamination of the vapor exiting the process waterstripper.
 12. The method of claim 8 wherein the neutralizing agent isinjected into the process water stripper line between the process waterstripper and the dilution steam generator at a concentration to keep thedilution steam generator blow down at a pH between about 9.5 and about10.5, thereby reducing corrosion of the dilution steam generator.
 13. Amethod for inhibiting fouling and corrosion of equipment in an ethyleneor styrene production plant, the method comprising injecting aneutralizing agent into a dilution steam system, the neutralizing agentcomprising a choline salt stabilized by about 2 wt. % to about 10 wt. %alkanolamine.
 14. A stabilized choline composition comprising a cholinesalt, a solvent, and from about 2 wt. % to about 10 wt. % of analkanolamine based on the total weight of the composition.
 15. Thestabilized choline composition of claim 14 wherein the choline salt hasa concentration from about 10 wt. % to about 50 wt. % based on the totalweight of the composition.
 16. The stabilized choline composition ofclaim 14 wherein the choline salt has a concentration from about 15 wt.% to about 25 wt. % based on the total weight of the composition. 17.The stabilized choline composition of claim 14 wherein the alkanolaminecomprises ethanolamine and the ethanolamine is present in aconcentration from about 3 wt. % to about 8 wt. % based on the totalweight of the composition.
 18. The stabilized choline composition ofclaim 17 wherein the ethanolamine is present in a concentration fromabout 4 wt. % to about 6 wt. % based on the total weight of thecomposition.
 19. The stabilized choline composition of claim 14 whereinthe solvent comprises water.